As this type of ball end mill having an even number of cutting edges, JP-A-2011-183532 proposes a ball end mill with six grooves, namely, 6-flute end mill, in which six radial cutting edges are formed on a front end portion of an end mill body, three of the radial cutting edges, which are adjacent to each other in the circumferential direction with one cutting edge interposed therebetween, among the radial cutting edges are long radial cutting edges (long cutting edges) that intersect with each other on the axis on the front end portion of the end mill body, and the other three radial cutting edges are short radial cutting edges (short cutting edges) that include inner peripheral ends at positions distant from the axis.
In this ball end mill, it is possible to easily form long radial cutting edges, which abut against each other on the axis at the front end of the end mill body, on a ball end mill of which all of the six radial cutting edges are long radial cutting edges, and to prevent chip clogging by securing the volume of a pocket that is used to discharge chips. Furthermore, in a ball end mill of which two radial cutting edges in the related art, which are disposed so as to face each other, are long radial cutting edges and the other four radial cutting edges are short radial cutting edges, many long radial cutting edges are present at the front end of the end mill body. Accordingly, it is possible to improve the accuracy of a machined surface and to lengthen the tool life.